1. Technical Field
The present disclosure relates to power supply circuit, and more particularly to a switching power supply circuit.
2. Description of Related Art
Switching power supply circuits are widely used in various electronic devices, such as liquid crystal display (LCD) monitors and televisions, for example.
Referring to FIG. 4, a typical switching power supply circuit 100 includes a power circuit 110, a switching circuit 101 and a load 130. The switching circuit 101 includes a power processing unit 120, a voltage divider circuit 150, a first filter circuit 160, a second filter circuit 170, and a capacitor C863. The first filter circuit 160, the power processing unit 120, and the second filter circuit 170 are electrically connected in series. The voltage divider circuit 150 includes a first resistor R885 and a second resistor R886. The first resistor R885 and the second resistor R886 are electrically connected in series between the load 130 and ground.
The power circuit 110 sends a DC voltage signal VDC to the first filter circuit 160. The first filter circuit 160 filters the voltage signal VDC to a stable signal VDC1, and sends the stable signal VDC1 to an input terminal Vin of the power processing unit 120. An output terminal Vout of the power processing unit 120 outputs an output voltage signal VDC2. The power processing unit 120 charges the capacitor C863, and the value of the output voltage signal VDC2 is increased gradually to substantially equal the value of the voltage signal VDC. The second filter circuit 170 filters the output voltage signal VDC2 to a driving voltage signal VDO. The driving voltage signal VDO is divided to generate a feedback voltage VDC3 through the voltage divider circuit 150, and the feedback voltage VDC3 is input to a feedback terminal FB of the power processing unit 120. The power processing unit 120 compares the feedback voltage VDC3 with a reference voltage Vref, if the feedback voltage VDC3 exceeds the reference voltage Vref, the output voltage signal VDC2 is forced into cutoff. If the feedback voltage VDC3 is lower than the reference voltage Vref, the output voltage signal VDC2 is forced into output.
The output voltage signal VDC2 instantaneously changes from high to low or low to high, however, the change of the current of the output voltage signal VDC2 is not instantaneous. During the gradual change of the current, the power of the output voltage signal VDC2 is dissipated. When the change of the output voltage signal VDC2 is at a high frequency, the power loss is more serious. The power dissipates in the form of heat, the circuit elements are easy to overheat and burn out.
What is needed is to provide a switching power supply circuit that can overcome the described deficiencies.